It is known that sewing machines for stockings and pantyhose comprise a roundabout with several tubular braces having the function of supporting and turning the stockings inside out, in which each tube is provided with two longitudinally sliding fins for transferring the tip of the stocking beyond the end of the tube on a horizontal rotating disk around its vertical axis, in a predetermined position with respect to a cutting machine. Said disk is associated with a suspended plate with alternating vertical motion with the function of holding, during the sewing, the tip of the stocking steady on the underlying rotating disk opposite the needle of the cutting machine. However, such a device of support and blocking of the stocking during the sewing presents the drawback whereby the arc of curvature of the sewing on the part of the sewing machine is directly connected to the radius of the disk and thus the variation of the curvature of the sewn tip is possible only by substituting the disk, which involves a loss of time which is incompatible with the production requirements of stockings or of pantyhose.